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Thread: Amperage readings on three phase 480/277v panel

  1. #1
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    Amperage readings on three phase 480/277v panel

    I have two panels in an office tower that are giving me weird amp readings with an amp probe. The panels are 480/277v and its only one breaker in one panel on the third floor and two breakers in a panel on the fourth floor. The amp readings from the amp probe jump around the one breaker is a three pole 100amp breaker it jumps between 25 amps and 59 amp every second. The second breaker is also 100amp three pole and it jumps between 15amps and 40amps every second. The last breaker is three pole 30amp breaker that feeds a v.a.v. heater it jumps from 6amps to 22amps. I'm trying to figure out why this is happening i have never seen anything do this before. it not tripping or nothing. No other panel or breaker in the office complex does this so i'm sure it's a local issue. just confused

  2. #2
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    What caused you to find this? Why were you doing an amp check?
    Tom
    TBLO

  3. #3
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    I was doing thermal imaging on the building. The breaker was hot.

  4. #4
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    Are they using solid state relay control on the electric heating? Not common from my experience but it is or was available.
    Tom
    TBLO

  5. #5
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    I'm not sure on the heating. This is a newer building and has been renovated within the last year on just about every floor.

  6. #6
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    Quote Originally Posted by njshaw189 View Post
    I was doing thermal imaging on the building. The breaker was hot.
    Are those the only "hot" breakers? Are those the only breakers exhibiting this bouncing amperage?

    What loads are on the first two 100A breakers?

  7. #7
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    A breaker with more load on it will be "hotter" then others that don't have as much load, especially if the load is fairly continuous.

    Does sound like possibly some solid state controlled heating circuit could be the source of such rapid cycling. Contactor controlled loads won't hold up to that kind of cycling.

    Trace down these circuits - if they are feeders you need to find the associated branch circuit(s) that are taking such current that is being questioned to find out what is going on.

    It might be more then one load involved but by the time you get to feeder level they add up to a fairly significant amount. Office tower - probably lots of laser printers in there - their "heaters" cycle frequently. Maybe not every second on an individual machine but put several in a large building and you will have constantly fluctuating load at feeder levels.

  8. #8
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    Quote Originally Posted by kwired View Post
    A breaker with more load on it will be "hotter" then others that don't have as much load, especially if the load is fairly continuous.

    Does sound like possibly some solid state controlled heating circuit could be the source of such rapid cycling. Contactor controlled loads won't hold up to that kind of cycling.

    Trace down these circuits - if they are feeders you need to find the associated branch circuit(s) that are taking such current that is being questioned to find out what is going on.

    It might be more then one load involved but by the time you get to feeder level they add up to a fairly significant amount. Office tower - probably lots of laser printers in there - their "heaters" cycle frequently. Maybe not every second on an individual machine but put several in a large building and you will have constantly fluctuating load at feeder levels.
    Copy machines too... I once did a legal office, I saw this exact thing and another electrician suggested it was the copy machines, they had 8 of them in a 30 room building! I unplugged them all, the issue went away, plugged them back in, current draw was high for the first 5 minutes, then started cycling like this again.
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  9. #9
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    Quote Originally Posted by Jraef View Post
    Copy machines too... I once did a legal office, I saw this exact thing and another electrician suggested it was the copy machines, they had 8 of them in a 30 room building! I unplugged them all, the issue went away, plugged them back in, current draw was high for the first 5 minutes, then started cycling like this again.
    yes, typical "toner" using copy machine is same thing as a laser printer when it comes to how they make that toner into print on the page.

  10. #10
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    I always thought it was an eye opener as to the fact that this law office had so many copy machines in one place. That was 25+ years ago however, before digital record keeping took off.
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